Preparation of cellulose esters



Patented Mar. 12,1940 a t f 2 193 033 UNITED STATES A N OFFWE 1 e PREPARATION OF CELLULOS E ESTERS Carl J. Malm and Loring W. Blanchard, J1'.,

. Rochester, N. Y., assignors to Eastman Kodak Company, Rochester, N. a corporation of New Jersey No Drawing. Application September 18, 1937,

l Serial No. 164,602.

3 Claims. (01. 260-227) This invention relates to a process for the sary. The third factor is avoided by the high production of organic acid esters of cellulose in activation of the cellulose by pretreating with whichrthe cellulose is pretreated with a solution a mixture of acetic and phosphoric acids. Anl of phosphoric acid in acetic acid and then esteriother object or our invention is to provide a 5- fled by adding acetic anhydride and sulfuric acid method in which cellulose of a high cuprammo- 5 catalyst thereto. In the production of high vism c y, sueh as is' y used in the cosity cellulose acetate it has been necessary to p ep n o g V e y cellulose esters, is limit the first stage or tetrachlorethane viscosity readily and evenly activated by the phosphoric to at least less than 100se'conds in order to obaeld it degrading e e ulosetain a product which was completely soluble in We have found that an acetic acid solution of 10 the reaction mixture to avoid gelling. Cellulose p sp fi exhibits a marked swelling aetlohf acetates of higher viscosity have been prepared, on cellulose which contributes to the smoothness However, in those cases it has been necessary to and uniformity of the subsequent esterification. incorporate a small amount of propionyl or bu- Our invention is employed by treating 081111 tyryl into the reaction mixture in order to get lose, such as o l s refilletl W P p, 15

a high viscosity product having high clarity. having a comparatively high euplemmonlllm We have found that this tendency of high viscosity, with an acetic acid solutio of Phosphoric cosity cellulose acetate, especially cellulose acea d, pr y d r the usual p tm n tate having a first stage or tetrachlorethane vis- Conditions The p at t qu d may con- 5 cosity of 100 seconds, as well as acetates of lower ta n ar q t e of phosphoric acid- It viscosity may be overcome by employing an acetic be a solution in which only a minor amount of acid solution of phosphoric acid to pretreat the phosphoric acid is present or a solution having cellulose prior to its esterification. We have approximately Phosphoric acid, based found that this not onlyincreases the solubility 0n e Weight of the acetic acid; v p

of the cellulose acetate in the esterificationbath, It is preferred 80011011116 leesehs that no 25 thus avoiding gelling, but also facilitates the reacm than a s u of p ph i a id be tion both by highly activating the cellulose withused, but this o tion depends of course out degrading it and by decreasing the absorpp the ratio Of llquidvtel cellulose p ye w tion by the cellulose of the acetyl sulfuric acid, It is o be understood t t activating b l s which is present in the esterification bath. 'w ity of the pretreatment solution does not increase 30 have also found that by employing phosphoric above Concentration of Phosphoric dacid, the reaction proceeds more smoothly so 1 A ter pretreatment the mass is subjected to the that the excessive cooling, which has been pres a t of acetic anhydride, u i a sulfuric acid viously necessary in the initial stages of the reac cataly With Without the d i f fu ther ticn, may be avoided.v l

The three things which. mainly contri t t methylene chloride. Prior to the addition of the gelling in th preparation of a, high viscosity esterifying reagents, which arepreferably cooled,

cellulose acetate are, v the mass is subjected to cooling so that the tem- L The excessive cooling which is necessary to perertule flees not rise t a Point which Will re- 46 control th reaction, I sult in too great a reduction in viscosity, as 40 2. The limited solvent power of the acetic aci otherwise the desired high viscosity cellulose toward cellulose triacetate. I ester Will not result- I 3 Uneven t mt The temperature will, as a rule, be maintained One object of our invention is to so affect these at not more than IF" although this w (16- ar, three factors that th gelling in the reaction pend upon the Proportion of sulfuric acid mixture is substantially eliminated. The first s is eemmenly'leeegnlzed. a t e amount factor is eliminated by the use of phosphoric of sulfuric acid present. based on e we ht of acid, in that thereaction is milder and proceeds the cellulose, 15 decreased e eh s the temmore smoothly than where nothing but acetic perature permissible without reducing viscosity.

acid, acetic anhydride and sulfuric acid catalyst The phy l procedure u in the p to are present in the esterif cation bath. As for ment of the cellulosein accordance with our inthe second factor, the phosphoric acid increases vention may be carried out in accordance with the solvent power of the acetic acid sufliciently the. process described and claimed in Malm apso that the triacetate is completely dissolved plication Serial No. 31,323. Example 11 illusacetic acid or other solvent, such as ethylene or 35 thereby under the temperature conditions necestratesa process in accordance with our inven- 55 85% phosphoric acid for l icuprammonium viscosity,

vWas cooled to 65 Example I F. A mixture of 1400' lbs. of

cotton 85%Qacetic anhydride and 32 lbs. of 98% sulfuric determined and it wasfound .II can be carried acid was added and the reaction was allowed to proceed up to a The dope which was obtained was free from haze and extremely viscous. To hydrolyze the ester, 850 lbs. of 50% acetic acid was added thereto and the mass was kept at 100 F. until the cellulose h'adan acetyl content of1 39%. The cellulose ester was then. precipitated, washed with pure water and dried. The transparency of the hydrolysis .mixture before precipitation was determined vand it was found. to be possible to see through 22 cm. of the solution. Similar reactions were carried out, except that in one case the phosphoric acid was omitted-and in the other those solutions was that it was possible to see through only 7-8.cm. of the solution or dope of the ester formed. I

Transparency .of

Example II -500 lbs. of refined sulfite pulp, having a high alpha cellulose content in sheeted form, was passed over a roll rotated in-acetic acid, containing-20% phosphoric acid. The sheet absorbed 140 lbs. of the pretreatment acid mixture. sheet was'then wound tightly and allowed to stand in an enclosed container at room temperature. for about-24 hours. The sheet was then fed into an acetylation mixer containing 3060 lbs. of acetic acid, 1400 lbs;

and 8000 cc. of sulfuric acid. This mixture had been cooled to 501 prior'to introducing the cellulose sheet. The reaction was allowed to proceed ma maximum-temperature of 100 F. In 4-5hours a-highly viscous dope of excellent claritywas obtained. Ihis ester was then hydroly'zed, precipitated and washed in the customary way.

If desired, the activatingtreatment of Example outloy passing'the cellulose sheet'over drying rolls before passing it over the roll moistened with the acetic acid-phosphoric acid mixture. This-will bring down the moisture content of the sheet and heat it to a temperature above 100F. If desired, the acetic acid mixture may also be kept above 100 Fu'by'passing steam through the applying roll or by placing steam coils in'the vat containing the acid mixture. If the emperature of pretreatment is kept at or above 100 F., a shorter pretreatment time, such as 6 hours or-even less, is sufficient.

Although the cuprammonium viscosityof the cellulose, employed as the starting material in the preparation of esters in accordance with our invention, is preferably high, nevertheless, our invention maybe made use of in the preparation of esters in which'cellulose, having a more modmaximum temperature of 100 F.-

' above 4%.

. cellulose acetateybutyrate.

' proportion anhydride and erate cuprammonium viscosity, is used. As the process, which we have described, has substantially no degrading efiect upon the cellulose or the ester prepared therefrom, a satisfactory cellulose ester may be prepared using'a medium viscosity cellulose. If a high viscosity cellulose is employed it might'even be desirable to lower this viscosity before the acetylation. be accomplished by adding a small amount of sulfuric acid to thepretreatment mixture toward the end of the pretreatment or during the cooling before the acetylation.

In the preparation of high viscosity esters, in accordance with our invention, it is desirablethat there be at least 3 parts of the esterification bath to every part of cellulose therein and that the proportion of sulfuric acid, which is used, be

It is also desirable that an esterification temperature be used which will not degrade the cellulose duringthe esterification and drop the tetrachlorethane-acetic acid first stage viscosity too much.

Our invention; although adapted for the preparation of cellulose acetate s,'particularly those of high viscosity, due to the diihculties met with in their preparation, it is also available in the preparing of other lower fatty acid esters of cellulose, such as cellulose acetate propionate or The swelling action of the phosphoric acid renders-the cellulose readily esterifiable and makes for a smooth esterification without danger of degrading the cellulose.

,Due to the extraordinary clarity of the solu tions of. esters prepared in accordance with our invention, these esters are especiallyadapted for 1. The processfor preparing organic acid esters oflcellulose which comprises pretreating the cellulose with a mixtureof acetic acid and a minor of phosphoric acidas the sole activating agent at atemperature between approximately 70 F. and approximately 100 thereby avoiding degradation of the cellulose, and subsequently esteriiyingthe cellulose .by adding a fatty acid sulfuric acid as the catalyst to the mass.

2. Theprocess for preparing organicacid esters of cellulose which comprises pretreating the cellulose with a mixtureof acetic acid and 20-30% of phosphoric acid as the soleactivating agent at a temperature of approximately 100 F., thereby avoiding degradation of thecellulose, and subsequently esterifying the cellulose by adding a fatty acid .anhydride and sulfuric acid as the catalyst to the mass.

3. The process for preparingcellulose acetate whichcomprises pretreating cellulosewlth a mixture of acetic acid and a minor proportion of phosphoric acid as the sole activating agent at atemperature between approximately 70 F. and approximately 100 F., thereby avoiding degradation of the cellulose, and subsequently acetylatingthecelluloseby adding acetic anhydride and sulfuric acid catalyst to'themass.

CARL J. MALM. .LORING W. .BLANCHARD, JR. 

